1. Field of the Invention
The present invention relates to a network system in which an image forming device connected to a server performs printing upon receiving print data from a client computer over a network, and more specifically to a print data processing system provided to the client computer.
2. Related Art
There have been known network printing systems in which an image forming device is connected to one of a plurality of personal computers (PCs) interconnected over a network so that the image forming device is available to all PCs connected to the network. The image forming device could be a printer, a multifunctional device having a printer function, or the like.
The present applicant has suggested in Japanese Unexamined Patent Application Publication No. 2003-131836 a network printing system with Windows (registered trademark), which is an example of operating system (OS), installed in client computers and also in a server.
Windows (registered trademark) provides Graphics Device Interface (GDI), which is a program module for representing graphical object. When a user designates to print document on application software, print data is prepared through the GDI. That is, the application sends draw commands to the GDI by calling functions for drawing functions of the GDI. The application therefore does not need to know the model and specifications of the image forming device used for printing, and the application can print to image forming devices in a variety of models with varying specifications by simply using the GDI. In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-131836 also, application software running on a client computer sends a print command to the GDI to generate print data to be sent to a server.
In the technology disclosed in Japanese Unexamined Patent Application Publication No. 2003-131836, when the application software sends a print command to the GDI to generate print data to be sent to the server, the GDI generates the print data in a format called an Enhanced Meta File (EMF). Print data in the EMF format is independent form a type of device, that is, not dependent on the model of the image forming device, and is thus more versatile than print data written in a device-dependent format enabling recognition by the specific final printer doing the actual printing (hereinafter referred to as “RAW data”). The EMF format makes it simple to process data and to create data.
Also, in this technology, the client computer creates data in the EMF format and then sends the same to the server. The server temporarily stores the received data in the EMF format as a spool file, and processes the spool file and/or extracts font data from the spool file as needed. Then, the server converts the data in the EMF format to RAW data recognizable by the image forming device and sends the RAW data to the image forming device for printing on paper or other recording medium.
However, sending data in the EMF format from the client computer to the server sometimes increases the amount of data that flows over the network to a large degree. This places a heavy burden on the network.
Because data in the EMF format is independent of the type of a target device, the data in the EMF format often contains much extra data that is not needed by the target device.
For example, data in the EMF format might contain color information even though a monochrome image forming device will be used for printing, or the print data might be high resolution print data even though a low resolution image forming device will be used for printing. In these cases, information that cannot be used effectively by the image forming device flows over the network, thereby placing unnecessary burdens on the network.
Also, data in the EMF format might contain redundant information to facilitate secondary processing. For example, in multipage printing called N-in-1 printing, such as 2-in-1 or 4-in-1 printing, N-number of successive pages is printed on a single sheet. However, in the EMF format, print data for the N-number of successive pages is not reduced to data for a single page (sheet). Instead, corresponding data includes print data for the N-number of successive pages and a command data for converting the print data to the N-in-1 format.
In addition, when printing a text, such as CONFIDENTIAL, over an original image, the text and the original image are superimposed one on the other and printed on a single sheet. However, data in the EMF format includes data for the text as a separate layer from data for the original image, but the data for the text and the data for the original image are not processed into print data for a single page.
This is convenient to further process the print data, such as to convert a 2-in-1 layout to a 4-in-1 layout, or to change the color of the text. However, this simply puts an unnecessary load on the network if further processing is unnecessary.